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American Institute of Aeronautics and Astronautics

1

Asteroid Mining

Kris Zacny1, Phil Chu

2, and Jack Craft

3

Honeybee Robotics, Pasadena, CA 91103

Marc M. Cohen4

Astrotecture™, Moffett Field, CA 94035-1000

Warren W. James5

V Infinity Research LLC, Altadena, CA, 91101

Brent Hilscher6

Hatch Engineering, Vancouver BC, Canada

This paper presents the results from the Phase 1 NASA Innovative and Advanced

Concepts (NIAC) investigation for the Robotic Asteroid Prospector (RAP). The project

investigated several aspects of developing an asteroid mining mission. It conceived a Space

Infrastructure Framework that would create a demand for in space-produced resources.

The resources identified as potentially feasible in the near-term were water and platinum

group metals. The project’s mission design stages spacecraft from an Earth Moon Lagrange

(EML) point and returns them to an EML. The spacecraft’s distinguishing design feature is

its solar thermal propulsion system (STP) that can provide for three functions: propulsive

thrust, process heat for mining and mineral processing, and electricity. The preferred

propellant is water since this would allow the spacecraft to refuel at an asteroid for its return

voyage to cislunar space thus reducing the mass that must be staged out of the EML point.

This paper focuses on mining and processing technologies.

Nomenclature

ARM = asteroid retrieval mission

ARProbe = Asteroid Reconnaissance Probe

EML = Earth-Moon Lagrange libration point

GNC = guidance, navigation, and control

GCR = galactic cosmic rays

ISRU = in situ resource utilization

LH2 = liquid hydrogen

LOX = liquid oxygen

PGM = platinum group metals

REE = rare earth elements

RAP = Robotic Asteroid Prospector

RTG = radio-thermal generator

TRL = NASA technology readiness level

1 Director, 398 West Washington Blvd, Suite 200, Pasadena, CA 91103, AIAA Life Member

2 Systems Engineer, 398 West Washington Blvd, Suite 200, Pasadena, CA 91103

3 Project Manager, 460 West 34

th Street, New York, NY 10001

4 President, Astrotecture™, NASA Research Park, Mail Stop 19-101, Moffett Field, CA 94035

5 President, V Infinity Research LLC, Altadena, CA, 91101, AIAA Associate Fellow

6 Senior Process Engineer, Hatch Engineering, Vancouver BC, Canada

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AIAA SPACE 2013 Conference and Exposition

September 10-12, 2013, San Diego, CA

AIAA 2013-5304

Copyright © 2013 by Kris Zacny, Marc Cohen, Warren James.. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.


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I. Introduction

HIS paper presents selected results from the nine-month, Phase 1 NASA Innovative and Advanced Concepts

(NIAC) investigation for the Robotic Asteroid Prospector (RAP). The central objective is to determine the

feasibility of mining asteroids. Ideally, this determination should be economic, technical, and scientific to lead to

the conceptualization of robotic and later human asteroid mining missions. The paper distinguishes resources that

can be used in space from those that could be brought back to earth and sold. The economic justification for the

latter is difficult to establish at present. The value of a resource in space should derive from not its value on Earth

but its usefulness in space. This value is analogous to the question: what is more valuable in the middle of Sahara

desert -- 1 liter of water or 1 kg of gold. The paper presents the identified commodity resources available in space

that are of potentially feasible economic interest, as well as a mining architecture and associated technologies for

exploiting those resources.

A. Accessible Resources

The RAP team identified water as the commodity most likely to be of value for extraction and sale to customers

in space for use as propellant. Platinum group metals (PGM) are the best candidates for potential sale on Earth,

however the scope of the undertaking would require returning refined platinum or other PGMs to Earth in the 10s of

metric tons. This amount of returned payload approaches 10% of the annual market. Given price elasticity, with an

increased supply of PGMs, their price will drop. Any calculations for the economics of returning PGMs to Earth

must take into account these supply effects on price.

Rare Earth Elements (REEs), although increasingly in demand on Earth, do not appear to be a viable candidate at

this time because of the high cost and complexity of processing the ore. Additionally since the current cost of REEs

extracted from the Earth is driven by the cost of the environmental remediation associated with that activity, there is

the very real chance that reducing those remediation costs would be a more cost effective way to increase the supply

of REEs than asteroid mining.

Future potential economic resources included scientific samples, regolith for radiation shielding, structural

elements such as Al, Fe, Si, and Ti for in space 3D printing, processed water for life support, radiation shielding, and

for propellant, and processed regolith for in space 3D printing of spacecraft structures. It should be noted that the

strength of 3D structures in space does not have to be very high. This is because loads these structures will see will

be relatively low. The required strength of spacecraft structures fabricated on Earth is driven by the launch loads and

landing loads in cases when spacecraft lands on another planet.

With respect to where to find these resources, the RAP proposal baselined a set of telescopes in Venus orbit,

looking outward from the Sun to identify and track the population of Near Earth Asteroids with far greater precision

than currently available. Therefore, the RAP team was delighted when Planetary Resources LLC announced their

startup in 2012, with a first phase of deploying the Arkyd space telescopes for this purpose. RAP looks forward to

data from advanced versions of the Arkyd that could obtain albedo, rotation and spectrographic data for candidate

asteroids.

B. Economics

The RAP team attempted to produce an economic demand model for the future “deep space economy,” based

upon a notion of the infrastructure for human habitation of deep space and the per capita consumption of resources

that infrastructure can produce and deliver in space. However, the team was unable to find sufficient economic data,

a verifiable economic model, or the expertise to perform this demand model study. For example, it is extremely

difficult to predict cost and schedule for developing metallurgical processes for PGMs extraction on Earth, let along

in space. Metallurgical processes developed for extracting and beneficiating ores on Earth in majority of cases where

result of years of “try and error” tests or luck.

Instead, as a starting point, the team decided to focus on water as the main resource (since extracting water is

much easier than extracting PGMs or other metals) and created a parametric analysis based more simplistically on

the price of water delivered to the International Space Station (ISS) from Earth and on the price of refined PGMs on

Earth. Factored against these prices and assumed market elasticity (how much the price might change with an

increase in supply) the team instead developed a parametric cost model to build, operate, and return the RAP

spacecraft and its payload to the Earth-Moon system.

C. Mission Design

For any interplanetary mission, the energy cost of the mission is driven by the orbital position of the departure

and destination objects. Having selected a destination, there is little flexibility in selecting a departure time.

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Moreover, the length of the synodic period between the Earths and Asteroids orbits drives the time between mission

opportunities, which can be extremely long, (i.e. decades or longer, for objects with similar orbit periods).

Therefore, the RAP mission architecture encompasses a highly flexible approach to defining mission opportunities

that uses multi-body gravity assists, multi-revolution interplanetary transfers and deep space maneuvers in order to

maximize the number of mission opportunities while minimizing total mission Delta V.

An important part of this approach is the use of an EML point as a staging point for departing and returning

mining spacecraft. This strategy provides significant reductions in Delta V when compared to missions departing

from or returning to LEO. This reduction occurs because the EML points are located at the edge of the Earth’s

gravity well and a vehicle there is only loosely tied to the Earth. This significantly reduces the propellant required

for those missions.

D. Spacecraft Design

The RAP team designed a prototype prospecting and mining spacecraft. It would implement a solar thermal

propulsion (STP) system incorporating parabolic solar concentrators that can concentrate sunlight to 10,000x the

incident insolation. The design of the RAP spacecraft enables use of this concentrated sunlight in three ways. First,

it provides heat at up to 2500K to the solar thermal engine to expand the fuel out the nozzle to create thrust. Second,

it provides process heat to the onboard mining, extraction, processing, and refining systems. Third, with a Stirling

cycle engine, it can generate about one megawatt of electricity.. Water would be the preferred fuel for the STP

system because it offers several advantages when compared to conventional propellants. Liquid water is very dense

when compared to its cryogenic by-products liquid oxygen (LOX) and liquid hydrogen (LH2). Not only does it not

require the complexity and cost of cryo-cooling, but also the mass and volume of the water tank structures can be

much smaller than the tankage required for a comparable mass of LOX and LH2. Moreover, water can be stored in

flexible tanks that simplify the task of propellant management in zero gravity. The RAP mission can launch these

empty tanks into space in a collapsed state, significantly reducing the size of the fairing needed for the launch

vehicle. The ultimate advantage of water as propellant for asteroid mining is that the RAP spacecraft can refuel

itself while on a mission from certain asteroids, thereby reducing the propellant loading required at the outset of the

mission.

E. Mining Technology

The mining approach varies a function of an asteroid size. For small asteroids of less than about 20 m in diameter,

the spacecraft may capture it with a system of gripping arms and airbags. The mining operation would involve

rendezvous with the target asteroid and orienting the spacecraft longitudinally at its pole along its axis of rotation.

The RAP spacecraft would then spin up to match the rotation of the asteroid and then attach at the pole. For larger

asteroids, the RAP will carry a set of small “spider” robots that can remove chunks of material from the asteroid and

place them into the intake hopper to begin the extraction process. For both approaches, we recommend using

Asteroid Reconnaissance Probes (ARProbes) to determine composition of the target asteroid and concentration of

water and other compounds of interest.

II. Commodities Feasible for Production in Space

A. Commodity: Water

The first tier of commodities (Commodity 1) for in space use would consist of water as propellant for cislunar

and interplanetary spacecraft. The demand for water for these applications, either to electrolyze into LOX and LH2

or to use directly as a propellant for solar thermal or nuclear thermal engines will become tremendous. This market

assumes that the water collected from carbonaceous chondrites, from regolith ice, or from chemically bound

sources, can serve as propellant with little or no post-extraction processing. In addition, water can be used to sustain

human presence in space (i.e. drinking water) though this market would not be as large as propellant market because

of the raw quantities required and over 90% of water can be recycled within a life support system. Water would also

prove highly useful as radiation shield integrated into the crew habitat structure (Cohen, 1997), although this market

is also subject to recycling of the water for shielding in other vehicles or for use in agriculture or life support.

B. Commodity : PGMs

Platinum group metals (PGMs) could potentially be valuable commodity on earth; however, it is impossible (at

least for now) to determine that with any certainty. There are two major unknowns. First, it is difficult to evaluate

the schedule and cost for developing metallurgical processes that will extract any of the PGMs in space. In fact, it is

extremely difficult to evaluate cost and schedule for developing of any metallurgical processes on Earth (let alone

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for space). Second, it is difficult to foresee the prices change of any of the PGMs given high supply and if new

markets of PGMs would be created as a result of price drop.

C. Commodity: Scientific Samples and Radiation Shielding

The second tier commodities of interest consist of regolith for radiation shielding in space and the same materials

excavated from the surface of the Moon, Mars, asteroids, Phobos, or Deimos for scientific samples. Once a true

cislunar, NEA, and interplanetary transportation system becomes available, the problem of delivering these

commodities to the customers in space will become greatly simplified. Eventually, it will not matter where is the

source of these and other commodities; the price to the customer will reflect that factor.

These scientific samples may include revolutionary, one of a kind new discoveries by deep space exploration

vehicles. However, what is more likely, they will consist of samples extracted, hermetically packaged and preserved

at suitable temperature, and returned for use in university and industry laboratories. The analogy to his type of

market might be Doc Ricketts in John Steinbeck’s Cannery Row (1945), who ran a business collecting specimens of

marine life and selling them to university, pharmaceutical, and other industrial labs. Of course, RAP will not expect

to find any life forms, but the idea is similar, to collect, process, and sell samples to researchers who are far from the

source.

D. Commodity: Regolith for Radiation Shielding

Radiation shielding has emerged time and time again as the leading barrier to humans living long-term or

permanently in deep space. During Mars Science Laboratory 253-day cruise to Mars, the Curiosity rover Radiation

Assessment Detector (RAD) absorbed about half a Sievert.

An alternative solution will be to attach regolith tiles or bricks to the exterior of a space habitat module.

Attaching these ISRU-produced shielding units can provide protection not only against the constant stress of GCRs,

but also micrometeoroids, and even enhance thermal stability, reducing the need for cooling and heat rejection.

E. Commodity: Water for Radiation Shielding

Water presents the unique advantage for radiation shielding that it is amorphous: as a liquid it has no

predetermined shape, as would be the case for regolith shielding. As a compound with a high content of loosely

bonded hydrogen atoms, water offers advantages both for higher linear energy transfer (absorption) and a lower

incidence of secondary particles compared to regolith. Although water shielding can be installed in the

environmentally controlled interior of a spacecraft, that solution comes with the downside that filling water bladders

will eat up much of the habitable volume within the spacecraft.

F. Commodity 5: Structural Materials

A critical milestone in establishing any type of settlement, colony, or civilization arises from the ability to build

its own shelter and patterns of settlement. For many decades, including throughout the period shown on the Space

Infrastructure Framework, only manufacturers on Earth will be able to produce pressure vessels for habitats in which

the crew can live and work safely, productively, and happily. However, there will be many secondary facilities,

structures, and civil works that the in space population will need. These facilities may range from a landing zone or

pad made from sintered regolith to aluminum fuel tanks, cranes or derricks to support mining, manufacturing,

fabrication, and assembly operations. These abundant structural materials include aluminum, iron, nickel, silicon,

and titanium, among many elements found on the celestial bodies of interest. As the space-based demand emerges

for new infrastructure on the surface of the Moon, Mars, or other bodies, the opportunity to source these facilities

mostly or entirely in space will arise, in competition with sourcing from Earth.

It should be noted that many structures could be 3D printed using regolith fines as feedstock. These structures do

not necessarily have to be as strong as on earth, since they will be used in zero gravity of space. In addition, the

main drivers for spacecraft structures build on earth are loads the structure will experience during the launch on top

of a rocket. Such loads will not be experienced in space, because the structure is already there. Another construction

application of regolith would be to sinter it under intense heat into a quasi-ceramic material. The sintered regolith

products could include ceramic masonry units (Allen, Graf, McKay, 1998), strengthened substrate on which to build

structures (Ruess, Schaenzlin, Benaroya, 2006), “paving” of selected to reduce dust interaction with robots, landers,

and crew, and possibly thermal insulation materials if it could include entrained gases.

G. Commodity 6: Water for Life Support and Agriculture

Commodity 1 exploited water for propellant with minimal post-extraction processing. For the life support

application, the water will need considerably more processing to make it fit for human consumption or for use in

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drinking, hygiene, laundry, and agriculture. This refinement of the ability to provide “the universal solvent” to the

deep space population will be a key to supporting and sustaining habitation permanently in deep space. Ideally,

space colonies will choose to locate close to a good source of water, in much the same way as early settlers on Earth

set up camp close to a river, spring, or other good source.

H. Commodity 7: Regolith for Soil

Regolith appears in Commodity 2 and 3 as a product for radiation shielding or scientific samples and feedstock

for 3D printing of structures. However, there is another, potentially larger demand for regolith in agriculture. Under

nearly all scenarios for deep space exploration, the crews will bring all the food they need with them from Earth.

Surely, they may grow some vegetables in an aeroponic “salad machine” or other such relatively compact devise,

but none of the prospective missions come close to thinking about self-sufficiency in food. Never the less, to

establish a permanent colony outside the Earth-Moon system, producing all or nearly all the food will become a

necessity for self-reliance and ultimately for survival. These colonies on the surface of a body with some gravity,

however slight, will not need to be limited to the aeroponics that are de rigeur in microgravity. Instead, they can

take advantage of the gravity – even partial G -- to feed water and nutrients to the plants’ root systems. Instead of

spraying water on the naked roots, these plants should be able to take root in a solid material. Certainly regolith

with no organic material – let alone humus – will hardly suffice for soil, it may be possible to process the regolith to

reduce or remove the reactivity of its oxides and other constituents such as perchlorates. Delivering regolith-derived

soil for agriculture at permanent colonies or bases could furnish a valuable market.

III. Mining and Processing Technology

The RAP mining strategy takes the form of Figure 1 the Hierarchy of Resources and Markets. It lays out the

tactical approach to each type of likely candidate resource and the corresponding markets on Earth and in space.

The Hierarchy of Resources and Markets shows that in general, the resources obtainable from Asteroids can be

divided into 4 broad categories: free water, bound water, metals, and regolith.

Figure 1. The Hierarchy of Space Resource Extraction and Markets.

It is a standard practice for terrestrial mines to organize mining operations around the main mineral product,

while collecting bonus revenues from ‘byproducts’ of lesser concentration. In a similar vein, we will not travel all

the way to an asteroid to mine just one resource. But neither will we be able to develop a “universal mining toolkit”

that can extract and process any and all ores that we find on an asteroid or anywhere else. We will need to match

particular technologies to specific deposits in selected locations. How do we align target body, the type of deposit,

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the mining technology, and what are the market and the price? On the other hand, the technology to grab and return

different types of asteroids will be similar.

We also need to change the way we think about valuable commodities, and recognize the influence of location

on value. Value on Earth does not equate to the same relative value in space. A simple analogy is this: What’s worth

more to a person stranded in the middle of a desert: a gallon of water or an ounce of gold?

A. Mining Functions

Mining of all types must follow these general steps: prospecting, excavating/mining, processing (e.g.

comminution, concentration), extraction, and storage. Table 1 explicates these steps. Comminution is an energy

intensive step and hence it should be avoided by mining pulverized regolith instead of small rocks or boulders.

Free water and bound water will be highly useful in the space environment for life support, radiation protection,

and propellant -- either as electrolyzed LOX/LH2 or as liquid water for Solar Thermal Propulsion. The controlled

extraction and processing technology associated with frozen water ice falls within the range of the relatively high

Technology Readiness Level of TRL 4 component or subsystem laboratory test for vacuum distillation (which the

RAP team accomplished during the 2012 NIAC Phase 1).

Table 1. Mining – Top Level Functions

Step Description Application to Asteroids

Prospecting Finding and defining the extent, location, and value of

the ore body.

Mineral concentration may be assumed to

be relatively uniform on asteroids, unless

some minerals are preferentially present in

the fine or coarse fraction of regolith.

Excavation Mining minerals from the ore body

Pneumatic methods

Magnetic methods (iron-nickel dust, nano-phase

iron)

Auger, scoop, etc.

Options include excavating and extracting

in situ, excavation ore for delivery to an

extraction plant, or capturing the entire

asteroid for delivery to an extraction plant.

Processing Comminution is a particle size reduction of materials.

It is extremely energy inefficient process and hence

should be limited or eliminated altogether.

Concentration is process of increasing the

concentration of the wanted minerals. This includes

magnetic and electrostatic separation.

Magnetic materials could be extracted using

magnetic concentration process. Only fines

should be captured using for example a

magnetic rake. Electrostatic separation will

be able to capture fines only and leave out

larger rocks.

Extraction Minerals:

Extraction of valuable metals from their ores through

chemical or mechanical means.

If carbonaceous chondrite – water plus

mineral extraction (titanium from Ilmenite,

nano-phase iron)

If metallic - difficult to de-alloy, hence use

iron-nickel dust for 3D printing (structures

can be much weaker in space than at 1g and

no launch loads)

Alloyed Metals:

If metals are present in alloy form (e.g. Nickel-Iron)

they must be de-alloyed.

Storage The refined resources is captured and stored within

protective enclosure

Volatiles could be pressurized. Water is

most likely going to be stored within

pressure cylinders (so that it could be easily

heated up and melted/sublimed). Processed

ore could be stored in sealed containers to

prevent losses.

Metals may be used in space to make structural components for spacecraft and spacecraft subsystems, or brought

back to Earth and sold. The most ready-to-hand approach would be to extract regolith dust or powder, feed it into a

3D printer, and then sintered into various components for spacecraft (e.g. fuel tanks), structures (e.g. trusses), and

habitats. Eventually, the technology will evolve to where it is possible to manufacture pressure vessel primary

structure that is equal to aluminum, steel, or titanium counterparts made on Earth. The technologies necessary to

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mine minerals or metals, to extract metals from minerals, to de-alloy metals (from M-type asteroids), or to mine

regolith and sinter it, are all at very low TRL. We do not know the cost to develop such technologies at present.

However, the RAP team believes that initially, we can pursue the “low-hanging fruit” to establish a sustainable

market. That low-hanging fruit is water.

Extracting free water is relatively easy – water ice can be sublimed and captured on a cold finger. Water

extraction from hydrous minerals requires more heat, and so presents more of a challenge to achieve, especially if

there is the potential for subsidiary reactions between liquid, vapor, or gaseous water and the materials from which

the process is attempting to separate it. An example is Anhydrite or anhydrous calcium sulfate (CaSO4) and

Gypsum (CaSO4·2H2O). When exposed to water, anhydrite readily transforms to the more commonly occurring

gypsum. This transformation is reversible at ~200°C under normal atmospheric conditions.

B. Asteroid Mining Approaches

Figure 2 shows our approach to asteroid mining. In general, we envisage that small, inexpensive, fully robotic

Asteroid Reconnaissance Probes or ARProbes, whether large or small, will initially study an asteroid, from orbit.

These probes would be deployed from the RAP mother spacecraft, fly to a nearby asteroid, acquire samples from

various locations, and fly back to the mother spacecraft. The analytical lab onboard the RAP mother spacecraft

would study each returned sample to determine the exact fraction of volatiles and minerals. This information would

then help the RAP operations team to determine the optimum extraction process and establish the initial value of the

extracted and processed material.

Figure 2. Asteroid Mining Approaches

After the initial reconnaissance step, the actual mining will proceed. The mining approach (and in turn the

mining spacecraft) will depend primarily on the size of the asteroid to be processed. If an asteroid is less than

approximately 20m in size, RAP could potentially “capture” the asteroid and process it in situ. There is an inherent

limitation to capturing and mining such a small object. Assuming that the asteroid is a carbonaceous chondrite with

the maximum expected water content of about 13%, the extractable water might not amount to a full return payload

or even approach it. However, if the target asteroid is large enough to yield a full payload of water, it will be much

too large to capture. In this scenario, the RAP mother spacecraft would deploy a team of smaller mining robot

spacecraft, called Spiders. These Spiders could either deliver feedstock material back to the RAP mother spacecraft

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for processing. More advanced Spiders might process material in-situ and deliver only processed material to the

RAP. Figure 3 shows a concept of the asteroid mining system: with Spiders and ARProbes.

Figure 3. The RAP Spacecraft carries Spiders and ARProbes

1. ARProbes

Figure 4 shows the Asteroid Reconnaissance Probe or ARProbe. This probe will acquire a small sample of the

asteroid’s surface material for analysis and determination of the regolith mineral grade, fraction of water present,

and whether it is a free water or bound water. ARProbes are fully robotic systems. They are small and inexpensive

and hence the RAP spacecraft could carry 10s or 100s of them.

Figure 4. Asteroid Reconnaissance Probe (ARProbe)

The notional concept of operations for sample return from the surface of an asteroid appears in the following

figures. The sequence begins with the parent spacecraft approaching the targeted asteroid. The parent spacecraft may

spend several weeks to months orbiting the asteroid and analyzing it with remote sensing equipment, including

cameras and stereo mapping. During this time, the RAP operations team will choose a potential landing site, based

on the data available. Following landing site selection, the ARProbe will detach from the spacecraft as shown in

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Figure 5, then uses its attitude control system to align itself for the descent towards the asteroid. The attitude control

system will initialize a spin stabilization routine to both stabilize the descent and to aid in penetration of the probe

into the asteroid surface. The onboard Guidance, Navigation and Control (GNC) system will control the impact

velocity and coordinates on the asteroid.

Figure 5. Concept of Operations – ARProbe Descent.

Flexibility will be highly desirable in final assignment of ARProbe excursions due to the relatively unknown

physical properties of asteroid surfaces. The RAP operations team will determine the velocity of the descent based

on results of laboratory testing, as well as visual and spectrographic imaging of the asteroid surface by the parent

spacecraft to determine surface characteristics. If the asteroid consists of a loose conglomerate of fine particles, the

RAP Ops team can command the velocity of the probe as relatively low. If the asteroid is dense, the RAP Ops team

can command high velocities to insure penetration and sample acquisition. This architecture allows for a broad

variety of asteroid surface characteristics.

Figure 6. Concept of Operations – ARProbe Impact and Sample Acquisition

4. Probe impacts surface of

Comet. Rotation and impact

causes auger flutes to fill

with sample. Foot pads

prevent over-penetration

5. Winch retracts auger and

casing. Shear pin holding

auger and casing in place

is sheared (if not already

sheared by impact)

6. Winch fully retracts

auger and casing

into Flipper

Mechanism. Spring

is preloaded

Shear Pin

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Following impact, the ARProbe sends a signal to the parent spacecraft alerting it to its successful contact and

sending a system status update. The ARProbe then uses a cable winch mechanism to pull the auger and casing out of

the asteroid and into the upper stage of the probe (Flipper Mechanism). When the auger and casing retract fully

retracted into the upper stage, they compress a spring,, maintaining tension on the cable.

Once the casing retracts fully into the upper stage, preloading the spring,, the Flipper Mechanism rotates the

entire canister and winch mechanism by 180 degrees. As soon as the Cap to the Casing is confirmed to be closed,

the upper stage (Asteroid Ascent Vehicle) detaches from the lower probe body and travels to the parent spacecraft as

shown in Figure 7.

Figure 7. Concept of Operations – Upper Stage Release from ARProbes Impactor Stage and Rendezvous

with a Parent Spacecraft.

2. Spiders

Spiders are robots that will follow to the asteroid surface after the ARProbes return their samples to the RAP

mother spacecraft. Spiders have multiple flexible legs with deep fluted augers mounted at the end of the legs. The

augers point inwards at an oblique angle. This geometry allows the spider’s legs to anchor itself to the asteroid

through a bracing action. In fact, the anchoring strength will only get stronger once the deep fluted augers are

deployed and engage the subsurface to capture the surface regolith. The spiders can acquire loose regolith and either

process it in situ or deliver it to the RAP spacecraft for processing.

The bracing system uses two or more multi-mode anchors positioned at an oblique angle to the surface as shown

in Figure 8, resulting in a net force component along the asteroid surface. This resultant force braces the spacecraft

to the surface. The advantage of this approach is that during the anchors’ deployment only the force component in a

vertical direction has to be overcome by, for example, firing rocket thrusters in the opposite direction.

C. Water Extraction

As Adam Smith (1776) stated famously “Nothing is more useful than water. . .” The same assertion holds true in

space: water can serve multiple purposes, so many in fact that it can reduce the “parts count” for some other

commodities or materials. These uses include propellant, life support, radiation shielding, and agriculture. Water

can serve as fuel (LOX/LH2) for high thrust combustion or as liquid for Solar Thermal propulsion); it can be used

for human consumption, and radiation protection. The in space propellant market – once it takes off – will bring a

voracious demand for water. The market for water for life support will be more constrained because life support

systems today achieve 90 to 95% recycling of water. The water for radiation shielding market will be similarly

constrained because shielding water makes an excellent candidate for recycling and reuse. Once a crewed spacecraft

returns to the Earth-Moon system on its last voyage (and presumably goes out of service), the crew can pump the

10. Marman Clamp is

actuated, releasing Upper

Stage from Probe Body

11. Probe takes off from Comet and guides itself

back to Spacecraft for rendesvous

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water from the old vehicle to a new one, or to storage tanks for future reuse. The market for water for agriculture

will include recycling, but as people begin growing their own food with a goal of self-sufficiency instead of

resupply, the demand for water will grow tremendously. Still, only the market for fuel will involve a straight

consumption demand, because once a spacecraft burns it or otherwise uses it up, a fresh supply becomes essential to

continue piloting the spacecraft.

Figure 8. The Bracing Anchor engages the surface at an oblique angle.

There are two ways to extract water: Mine-Transport-Extract or Mine-Extract In Situ.

1. Captive Recovery (Mine-Transport-Extract)

First, an asteroid can be placed inside a bag and sealed. The RAP directs concentrated sunlight from from Solar

Concentrators light directly into the bag. Coated on the inside with a reflective coating, the bag’s interior helps to

spread the light and thus the heat evenly. . Once the water in the captive asteroid starts to sublime, it will create its

own pressure. The pressure difference between the bag and the condenser (cold finger) where the water is captured

does not have to be high to channel the vapor into the condenser. Water extraction tests conducted in a vacuum

chamber showed that a pressure difference of approximately 500 Pa was sufficient (Zacny et al., 2012). In addition,

heat recovered from the condenser unit could be pumped back into the bag to enhance extraction efficiency.

2. In Situ Recovery (Mine-Extract In Situ)

The second method of water extraction, vacuum distillation, is to capture regolith that contains ice onto deep

auger flutes. Figure 9 shows the several steps required to capture water. When the auger digs fully into the frozen

regolith, it acquires the load of material for processing. Once fully loaded, the augur withdraws from the hole it

drilled in the regolith and then retracts into a reactor. Heat from an RTG, electrical heater, or directed concentrated

sunlight can then heat up the icy-soil to 0 °C. Further heating will allow ice to sublime and be captured on a cold

finger. This particular technology has already been proven in vacuum and showed to work well (Zacny et al., 2012).

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Figure 9. Water Extraction and Condensation Process

Table 2 shows the results of a feasibility study to determine the key parameters for water extraction from an

Asteroid. The variables include the mass fraction of water in the asteroid, efficiency of a reactor (fraction of water

captured inside a reactor), number of reactors, and size of an asteroid. To make the calculations easier to

understand, the table uses 100 kg of water as an initial parameter – that is, the mission requires extracting 100 kg of

water. In order to recover so much water, the RAP spacecraft (bagging) approach, would require an asteroid to be at

least 3 meter in diameter. This metric assumes asteroid has 10wt% water and 50% of that is recoverable. Our

estimates did not include the time required to accomplish that extraction – this is a fraction of energy that solar

concentrators can deliver to the bag.

On the other hand, a Spider with 8 water distillation reactors, each 20 cm diameter and 1 m long, would require

3.3 days to capture 100 kg of water (assuming the same wt% water and efficiency cycle). This finding assumes 1

hour per each drill/capture regolith/extract water cycle. The energy required to sublime 100 kg of water with 90%

energy efficiency is 83 kWh.

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Table 2. Water Extraction Feasibility Calculations

The RAP spacecraft will be configurable to support either the asteroid capture strategy for captive sublimation or

the Spider strategy for vacuum distillation. Figure 10 shows the required diameter of an asteroid for the RAP

spacecraft concept and the duration of Spider cycles (for Spiders) required to recover 100 kg of water as a function

of the water weigh % in the asteroid regolith. As the fraction of water in an asteroid increases, the required mass of

an asteroid or duration of an 8-legged Spider cycle decreases. Note the maximum water fraction is 22% (Norton,

2002).

Figure 10. Diameter of an asteroid for the RAP spacecraft or duration of Spider cycles required to recover

100 kg of water as a function of water wt% in asteroid regolith. Water extraction efficiency assumed at 50%

in both cases.

1% 2% 5% 10% 20% 22%

Percentage of water captured inside reactor 50% 50% 50% 50% 50% 50%

Percentage of water recovered from an asteroid 0.50% 1% 2.50% 5% 10% 11%

Required mass of asteroid tons 20 10 4 2 1 0.9

Bulk density of asteroid g/cc 1 1 1 1 1 1.0

Required volume of asteroid m3 20 10 4 2 1 0.9

Diameter of required spherical asteroid m 3 2 2 1 1 1

Auger (Reactor) diameter m 0.20 0.20 0.20 0.20 0.20 0.20

Auger (Reactor) length m 1 1 1 1 1 1

Auger (Reactor) volume m3 0.03 0.03 0.03 0.03 0.03 0.03

Number of Augers/Reactors (i.e. Spider legs) 8 8 8 8 8 8

Number of spiders 1 1 1 1 1 1

Total volume captured m3 0.25 0.25 0.25 0.25 0.25 0.25

Total mass captured ton 0.25 0.25 0.25 0.25 0.25 0.25

Total water captured ton 0.00 0.00 0.01 0.01 0.03 0.03

Number of auger mining cycles 80 40 16 8 4 4

Time per cycle hr 1 1 1 1 1 1

Duration of water capture hrs 80 40 16 8 4 4

Duration of required water capture cycles days 3.3 1.7 0.7 0.3 0.2 0.2

Water weight % in asteroid

RAP (Asteroid Bagging Option)

Spiders (for larger asteroids)

Percentage of Water Recoved from an Asteroid

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D. Metal Mining

Metal recovery in space will be extremely challenging. On Earth, gravity and water are key constituents of most

terrestrial extraction and processing technologies. In addition, on Earth, the majority of metals occur in the form of

various minerals and oxides. They need to be liberated and purified though a number of chemical processes. For

example, Ilmenite is a crystalline iron titanium oxide (FeTiO3). Standard mining processes extract Titanium from

the Ilmenite by the following set of reactions:

FeTiO3 (s) + 3Cl2 (g) + 3C(s) 3CO (g)+ FeCl2 (s) +TiCl4 (g) (1)

TiCl4 (g) + 2 Mg (s) 2MgCl2 (l) + Ti(s) (2)

Terrestrial metal extraction and refining technologies took centuries to developed and implement to a level that

makes them economically viable. For example, until Hall and Héroult developed a process for the production of

aluminum, the metal was more expensive than silver. However, it took much experimentation to arrive at the best

formula. The paragraph below bears witness to the complexity of the aluminum extraction process. The recipe does

not include many details that go into making sure this process works, however, it does give a ‘taste’ of complexity.

In the Hall–Héroult process alumina, Al2O3, is dissolved in an industrial carbon-lined vat of molten cryolite,

Na3AlF6 (sodium hexafluoroaluminate), called a "cell." Passing a direct electric current through it then electrolyzes

the molten mixture of cryolite, alumina, and aluminum fluoride. The electrochemical reaction causes liquid

aluminum metal to be deposited at the cathode as a precipitate, while the oxygen from the alumina combines with

carbon from the anode to produce carbon dioxide, CO2. The liquid aluminum is taken out with the help of a siphon

operating with a vacuum, in order to avoid having to use extremely high temperature valves and pumps. The liquid

aluminum then may move in batches or via a continuous hot flow line to where it is cast into aluminum ingots.

The electrolysis process produces exhaust that escapes into the fume hood to be evacuated from the working

process environment. This exhaust is primarily CO2 produced from the anode consumption and hydrogen fluoride

(HF) from the cryolite and flux. HF is a highly corrosive and toxic gas, even etching glass surfaces.

Unfortunately, at this time there is no rule of thumb or a golden formula to determine how much investment and

how many years is required to develop certain metallurgical process. This uncertainty is one of the major problems

in extracting metals from Asteroids. Even if the target is an all-metallic M-type asteroid, asteroid miners will need to

develop a process to de-alloy the asteroid (M type asteroids are made principally of an iron-nickel alloy). Metal

alloy separation into individual metals is a complicated task, and is not feasible in space environment at this time. A

simple, robust, lightweight, automated system for metal extraction and processing in space has yet to be conceived..

Potentially, one could skip the de-alloying step by processing the existing asteroid alloy into steel or other alloys,

presumably by adding ingredients to it, heating, stirring, and cooling.

In addition to the complexity in developing any metallurgical process, the fact that the technology must work in

microgravity and probably in a low pressure environment as well means that it require testing in LEO. Flying such

complex and potentially hazardous experiments to the International Space Station would be extremely expensive;

such research and testing would add millions of dollars and years to the R&D cost and schedule. In summary, it is

extremely difficult to develop a metallurgical process for the terrestrial environment and it will be exponentially

more difficult to do so for the space environment. These challenges contribute to the skepticism that mining REEs or

PGMs would ever become profitable.

On the other hand, the space environment may offer some advantages, at least in the utilization of space-

produced structural components. The spacecraft needs to be sufficiently robust to withstand launch loads at the top

of a rocket. However, once in space, most components do not see major loading, save for a few (e.g. pressurized

fuel tanks). Hence, space structures could in fact be made lighter weight and thus weaker since they would not need

to withstand launch loads. In that case, 3D printing technology might well be suitable for space environment,

particularly 3D printed elements have yet to come close to achieving the strength properties of metal forgings or

laminated composites. In 3D printing, a feedstock material in the form of fine powder is heated up and melted and

then printed layer-by-layer to form a structure. The feedstock to a space 3D printer could be fine asteroid regolith or

a powdered metal. Such regolith could be mined with relative ease using magnetic or pneumatic mining techniques.

A concept of mining using magnetic rakes has been proposed before as well (Hartmann, 2000; Kuck, 1995). A

magnetic systems, just as pneumatic systems, minimize moving parts and hence enhance robustness and reliability,

which is vital when dealing with small and often abrasive dust. Since M-type asteroids contain magnetic Kamacite

and Taenite, the magnetic mining could be very efficient. Of course other types of asteroids could also be targeted

for metallic powders. Pneumatics can provide a method not only to collect but also concentrate the loose particulates

from an asteroid, with gas recovery to enhance efficiency. Recent testing in the Honeybee Robotics laboratories

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revealed that 1g of gas at 50 kPa absolute could loft over 5000 grams of regolith in vacuum at high velocities.

Unlike a magnetic system, a pneumatic system would work with any types of powder and it will provide required

cut off particle sizes.

Finally the prospective demands of the in space commodities market can change the relative values and prices of

commodities to different relationships than their prices on Earth. Presumably, the value of commodities in space

will be established based on their usefulness in space rather than their price on earth. For example, aluminum is a

much better structural material than gold, and in turn would be more valuable in space (even though it cost less than

gold on earth).

IV. Conclusion

Technology for asteroid mining and processing is currently at very low TRL. Extracting asteroid surface

materials is easier to do since it is more or less a mechanical/physical process and could be accomplished via various

means such as magnetic, pneumatic, mechanical (scoop, rake, drill) etc. These approaches could be modeled and

tested in zero-g flights and vacuum chambers.

Processing of regolith to extract free-water is at TRL 3-4 and has been demonstrated in vacuum. Since water

vapor pressure and not gravity drives water extraction, vacuum-chamber tests in 1G can apply to the asteroid

environment as well.

Metal extraction or de-alloying technologies are at TRL 1, basic principles observed. Metallurgy (the science of

extracting and purifying valuable resources) does not offer a parametric equation to determine the time and cost for

developing new extraction technology. Hence, it is extremely difficult to determine how much cost, how long a

time, and even “if” a we can develop a for extracting and purifying metals on asteroid. Since potential technologies

would have to be tested in zero-g, the cost and schedule for such a technology development would need to take these

procedural bottlenecks into account.

Collecting regolith fines and printing 3D structures in zero-g would be feasible since 3D printing relies on a

physical (melting/sintering) rather than a chemical process. MicroG prototypes could be developed and tested in

microG parabolic flight planes and on the exterior experiment platforms of ISS (i.e. vacuum and zero-g).

Precious metal ores occur naturally at very low concentrations; that low concentration is a large part of what

makes them rare and valuable. In terrestrial mining, the whole point of beneficiation, concentration, and the other

processes on-site at the mine are to separate the ore from the slag, so that the expense of transport applies only to the

useful ore. The same principle applies to Space Mining. There is no profit in returning the slag to the Earth-Moon

system, only huge added costs. Therefore, we do not see an economic model for returning a whole asteroid to the

Earth-Moon System, with the possible exception of capturing one for use as a testbed for mining technologies. This

finding carries profound implications for the “Asteroid Retrieval Missions” (ARM).. This finding means that there

is no realistic economic return in an ARM.

However asteroid retrieval may bring other, non-pecuniary returns. Such a mission may offer these benefits:

Asteroid retrieval would be a fabulous engineering and operations challenge that will stretch and

strengthen in space operational capability.

The scientific value to examining a complete asteroid in depth, even a small one, could be immense.

This investigation can inform the design of future asteroid exploration spacecraft and their missions.

The asteroid can provide a testbed for astronaut training, providing great value in understanding the

capabilities they will need on such a deep space mission.

Most obviously, the retrieved asteroid can serve as a testbed for advanced prospecting, mining,

extraction, and processing technologies in microgravity.

Despite all these inspiring and idealistic purposes for the retrieved asteroid, the RAP team could not find any

scenario for a realistic commercial economic return from such a mission. The only scenario for making a profit

appears to be all in situ mining, extraction, and processing to enable the delivery of finished products or

commodities to the customers who will want them and pay for them.

Acknowledgments

This work was funded by the Phase 1 NASA Innovative and Advanced Concepts (NIAC) Contract No.

NNX12AR04G

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